This invention relates to a liner for rehabilitating an underground piping system, and in particular, to a stretchable fabric that provides improved strength and stiffness for such rehabilitations. This invention also relates to a method of manufacturing such a stretchable fabric. The invention is useful in the repair and rehabilitation of piping systems that are damaged and/or deteriorated.
Underground piping systems are essential for transporting liquids and gases to homes and businesses. Utilities typically use these piping systems for sewer, water, gas, and other applications. Such piping systems are installed several feet underground and access to the piping systems is therefore limited.
Underground pipes experience cyclical loadings, premature wear, corrosion, porosity, and ambient foundation or earth movements. These factors contribute to the overall deterioration of the pipes. Often the pipes develop damaged or weakened areas requiring repair.
To maintain the service afforded by the underground piping system, any cracks or leaks must be promptly detected and repaired. Such repair generally requires the replacement of a long length of the pipe, since the repair of a small section of the pipe by welding, patching or otherwise, is usually unsatisfactory and difficult or even impossible because the pipe diameter does not allow human access in safe conditions. In the case of an underground pipe, the replacement of the pipe is difficult, expensive, and time consuming.
A solution for the repair of underground pipes is to repair a pipe while it is still in place. In-situ pipe repair procedures have been developed. Some procedures include the insertion of a pliable reinforcement liner into the damaged pipe. The liner typically has an outer diameter which is substantially the same as the inner diameter of the damaged pipe. The liner is pressurized so that it presses firmly along the inner wall of the damaged pipe. The expanded liner is then cured to form a new, rigid lining or surface within the original pipe.
There are several types of reinforcement or reinforcing liners. Some liners are made from a polyester material. Other liners utilize fibers that are impregnated with a synthetic resin. Fibrous mats are alternatively used as the material for a liner. Some reinforcement liners include glass fibers for support and strength, since glass fibers have a high strength and stiffness, while still possessing good resistance to elongation.
Some liners are hardened or cured after they have been installed. These liners are referred to as xe2x80x9ccured-in-place (CIPP)xe2x80x9d liners. The resin in a cured-in-place liner bonds or adheres to the glass or other reinforcement fibers after it is cured. Due to the bond between the resin and the fibers, the resin also becomes more resistant to stretching when axial or radial loads are applied to the cured liner. Thus, the cured resin is reinforced by fibers so long as the bond between the resin and glass fibers is not broken.
The liners are typically installed in environments that are continuously exposed to water and other corrosive materials. In particular, sewer pipelines, due to the presence of anaerobic bacteria develop hydrogen sulfide which, by oxidation develops diluted sulfuric acid in sewage water. These liners are also exposed to varying temperatures and flow conditions.
The liner inserted inside a pipe should have good flexibility to stretch and adjust itself to the host pipe diameter before cure, and must have good strength characteristics and adequate stiffness after cure to resist ground settlement or ground movement particularly if the host pipe has lost its required structural integrity.
Several different materials can be used as a liner to reinforce a pipe. An example of a known reinforcing material is disclosed in U.S. Pat. No. 5,535,786 to Makela et al (‰MakelaÂ). Makela discloses a material for reinforcing a flow conduit. The material includes a knitted fabric 5 and a felt layer 6 that are coupled together. Fabric 5 and layer 6 can be impregnated by a resin. As shown in FIG. 5 of Makela, fabric 5 includes filaments 3 that extend in the peripheral direction of the conduit for radial strength. Fabric 5 also includes yarn 1 that is formed with loops 2. Fabric 5 is an interlock or double-knitting type fabric in which the reinforcement filaments extend in a mutually parallel relationship through the loops 2.
Another example of a reinforcing liner is shown in U.S. Pat. No. 5,868,169 to Catallo (‰CatalloÂ). Catallo discloses a tubular lining hose for rehabilitating a pipe. The lining hose 1 includes layers of resin absorbing material 2 and 4, a reinforcing fiber layer 3, and an outer covering layer 5.
Catallo discloses several embodiments of the lining hose. As shown in FIG. 1 of Catallo, the reinforcing fiber layer 3 includes longitudinal fibers 31 and radial fibers 32. A second embodiment, shown in FIG. 2, includes spaced radial fibers 34 which are separated by a distance greater than fibers 32. In FIG. 3, the fibers in layer 3 are oriented in a crisscross helical pattern. Finally, in FIG. 4, layer 3 includes randomly oriented fibers 40 that are held together by cross-hatched stitching 42. The randomly oriented fibers 40 form a chopped strand mat.
Another example of a reinforcing lining is shown in U.S. Pat. No. 3,996,967 to Takada (‰TakadaÂ). Takada discloses a reinforcing matrix 3 that includes longitudinally extending fibers 1 and peripheral fibers 2, as shown in FIG. 1 of Takada. Fibers 1 are glass fibers which have a low elongation property. The peripheral fibers 2 have a high non-recoverable elongation and can be an unstretched polyester. Fibers 2 are non-recoverable to retain the shape of the lining once the lining has been set.
A need exists for an economical reinforcing material that is flexible to accommodate different applications. Similarly, a need exists for a reinforcing liner that provides hoop tensile and bending strength as well as hoop bending stiffness while being stretchable in its circumferential direction to fit to the inner diameter of the host pipe.
The shortcomings of the prior art are overcome by the disclosed reinforcement liner and methods of manufacturing the liner. The liner includes a fabric material having first and second support layers. Each of the layers includes reinforcing fibers. The first and second support layers are oriented in different directions to provide support to the liner in those directions.
The liner includes a stitching material that is used to couple the first and second support layers together. The stitching material is preferably an elastic yarn.
One of the support layers includes long, chopped strands that are oriented parallel to each other. The long, chopped strands are directed so that they are in the peripheral direction of the finished reinforcement liner. The long, chopped fibers can be distributed continuously or only along portions of the width of the fabric.
The disclosed methods of manufacturing a liner include alternative processes by which the liner can be made. The fabric is manufactured in the form of a continuous roll. One method involves winding the roll in a helical pattern about a fixed mandrel. Another method involves mounting several rolls circumferentially about a mandrel. The rolls are mounted so that strips of fabric from each roll overlap a portion of adjacent fabric strips to provide a continuous liner surface on the mandrel.